Marijke M Westra

Leukocyte Cathepsin S Is a Potent Regulator of Both Cell and Matrix Turnover in Advanced Atherosclerosis

Objective—A dysbalance of proteases and their inhibitors is instrumental in remodeling of atherosclerotic plaques. One of the proteases implicated in matrix degradation is cathepsin-S (CatS). To address its role in advanced lesion composition, we generated chimeric LDLr−/− mice deficient in leukocyte CatS by transplantation with CatS−/−×LDLr−/− or with LDLr−/− bone marrow and administered a high-fat diet. Methods and Results—No difference in aortic root lesion size could be detected between CatS+/+ and CatS−/− chimeras. However, leukocyte CatS deficiency markedly changed plaque morphology and led to a dramatic reduction in necrotic core area by 77% and an abundance of large foam cells. Plaques of CatS−/− chimeras contained 17% more macrophages, 62% less SMCs, and 33% less intimal collagen. The latter two could be explained by a reduced number of elastic lamina fractures. Moreover, macrophage apoptosis was reduced by 60% with CatS deficiency. In vitro, CatS was found to be involved in cholesterol metabolism and in macrophage apoptosis in a collagen and fibronectin matrix. Conclusion—Leukocyte CatS deficiency results in considerably altered plaque morphology, with smaller necrotic cores, reduced apoptosis, and decreased SMC content and collagen deposition and may thus be critical in plaque stability.

CXCR4 blockade induces atherosclerosis by affecting neutrophil function

AIMS The SDF-1α/CXCR4 dyad was previously shown by us and others to be instrumental in intimal hyperplasia as well as early stage atherosclerosis. We here sought to investigate its impact on clinically relevant stages of atherosclerosis in mouse and man. METHODS AND RESULTS Immunohistochemical analysis of CXCR4 expression in human atherosclerotic lesions revealed a progressive accumulation of CXCR4(+) cells during plaque progression. To address causal involvement of CXCR4 in advanced stages of atherosclerosis we reconstituted LDLr(-/-) mice with autologous bone marrow infected with lentivirus encoding SDF-1α antagonist or CXCR4 degrakine, which effects proteasomal degradation of CXCR4. Functional CXCR4 blockade led to progressive plaque expansion with disease progression, while also promoting intraplaque haemorrhage. Moreover, CXCR4 knockdown was seen to augment endothelial adhesion of neutrophils. Concordant with this finding, inhibition of CXCR4 function increased adhesive capacity and reduced apoptosis of neutrophils and resulted in hyperactivation of circulating neutrophils. Compatible with a role of the neutrophil CXCR4 in end-stage atherosclerosis, CXCR4 expression by circulating neutrophils was lowered in patients with acute cardiovascular syndromes. CONCLUSION In conclusion, CXCR4 contributes to later stages of plaque progression by perturbing neutrophil function.

Vascular neuropeptide Y contributes to atherosclerotic plaque progression and perivascular mast cell activation.

AIM Neuropeptide Y is an abundantly expressed neurotransmitter capable of modulating both immune and metabolic responses related to the development of atherosclerosis. NPY receptors are expressed by a number of vascular wall cell types, among which mast cells. However, the direct effects of NPY on atherosclerotic plaque development and progression remain to be investigated. In this study we thus aimed to determine whether NPY is expressed in atherosclerotic plaques and to establish its role in atherosclerotic plaque development. METHODS AND RESULTS NPY expression was seen to be increased up to 2-fold in unstable human endarterectomy plaques, as compared to stable plaques, and to be significantly upregulated during lesion progression in apoE(-/-) mice. In apoE(-/-) mice focal overexpression of NPY in the carotid artery significantly increased atherosclerotic plaque size compared to controls, while plaque composition was unaffected. Interestingly, perivascular mast cell activation was significantly higher in the NPY-overexpressing mice, suggesting that NPY may impact plaque progression in part via mast cell activation. Furthermore, in vitro NPY-induced murine mast cell activation resulted in the release of pro-atherogenic mediators including IL-6 and tryptase. CONCLUSIONS Our data show that NPY expression is increased during atherogenesis and in particular in unstable plaques. Furthermore, perivascular overexpression of NPY promoted plaque development and perivascular mast cell activation, suggestive of a role for NPY-induced mast cell activation in lesion progression.

Hematopoietic G-protein-coupled receptor kinase 2 deficiency decreases atherosclerotic lesion formation in LDL receptor-knockout mice

Leukocyte chemotaxis is deemed instrumental in initiation and progression of atherosclerosis. It is mediated by G‐protein‐coupled receptors (e.g., CCR2 and CCR5), the activity of which is controlled by G‐protein‐coupled receptor kinases (GRKs). In this study, we analyzed the effect of hematopoietic deficiency of a potent regulator kinase of chemotaxis (GRK2) on atherogenesis. LDL receptor‐deficient (LDLr–/–) mice with heterozygous hematopoietic GRK2 deficiency, generated by bone marrow transplantation (n=15), displayed a dramatic attenuation of plaque development, with 79% reduction in necrotic core and increased macrophage content. Circulating monocytes decreased and granulocytes increased in GRK2+/– chimeras, which could be attributed to diminished granulocyte colony‐forming units in bone marrow. Collectively, these data pointed to myeloid cells as major mediators of the impaired atherogenic response in GRK2+/– chimeras. LDLr–/– mice with macrophage/granulocyte‐specific GRK2 deficiency (LysM‐Cre GRK2flox/flox; n=8) failed to mimic the aforementioned phenotype, acquitting these cells as major responsible subsets for GRK2 deficiency‐associated atheroprotection. To conclude, even partial hematopoietic GRK2 deficiency prevents atherosclerotic lesion progression beyond the fatty streak stage, identifying hematopoietic GRK2 as a potential target for intervention in atherosclerosis.—Otten, J. J. T., de Jager, S. C. A., Kavelaars, A., Seijkens, T., Bot, I., Wijnands, E., Beckers, L., Westra, M. M., Bot, M., Busch, M., Bermudez, B., van Berkel, T. J. C., Heijnen, C. J., Biessen, E. A. L. Hematopoietic G‐protein‐coupled receptor kinase 2 deficiency decreases atherosclerotic lesion formation in LDL receptor‐knockout mice. FASEB J. 27, 265–276 (2013). www.fasebj.org

Hematopoietic sphingosine 1-phosphate lyase deficiency decreases atherosclerotic lesion development in LDL-receptor deficient mice

Aims Altered sphingosine 1-phosphate (S1P) homeostasis and signaling is implicated in various inflammatory diseases including atherosclerosis. As S1P levels are tightly controlled by S1P lyase, we investigated the impact of hematopoietic S1P lyase (Sgpl1−/−) deficiency on leukocyte subsets relevant to atherosclerosis. Methods and Results LDL receptor deficient mice that were transplanted with Sgpl1−/− bone marrow showed disrupted S1P gradients translating into lymphopenia and abrogated lymphocyte mitogenic and cytokine response as compared to controls. Remarkably however, Sgpl1−/− chimeras displayed mild monocytosis, due to impeded stromal retention and myelopoiesis, and plasma cytokine and macrophage expression patterns, that were largely compatible with classical macrophage activation. Collectively these two phenotypic features of Sgpl1 deficiency culminated in diminished atherogenic response. Conclusions Here we not only firmly establish the critical role of hematopoietic S1P lyase in controlling S1P levels and T cell trafficking in blood and lymphoid tissue, but also identify leukocyte Sgpl1 as critical factor in monocyte macrophage differentiation and function. Its, partly counterbalancing, pro- and anti-inflammatory activity spectrum imply that intervention in S1P lyase function in inflammatory disorders such as atherosclerosis should be considered with caution.

Leukocyte Bim deficiency does not impact atherogenesis in ldlr -/- mice, despite a pronounced induction of autoimmune inflammation

Proapoptotic Bcl-2 family member Bim is particularly relevant for deletion of autoreactive and activated T and B cells, implicating Bim in autoimmunity. As atherosclerosis is a chronic inflammatory process with features of autoimmune disease, we investigated the impact of hematopoietic Bim deficiency on plaque formation and parameters of plaque stability. Bim−/− or wild type bone marrow transplanted ldlr−/− mice were fed a Western type diet (WTD) for 5 or 10 weeks, after which they were immunophenotyped and atherosclerotic lesions were analyzed. Bim−/− transplanted mice displayed splenomegaly and overt lymphocytosis. CD4+ and CD8+ T cells were more activated (increased CD69 and CD71 expression, increased interferon gamma production). B cells were elevated by 147%, with a shift towards the pro-atherogenic IgG-producing B2 cell phenotype, resulting in a doubling of anti-oxLDL IgG1 antibody titers in serum of bim−/− mice. Bim−/− mice displayed massive intraplaque accumulation of Ig complexes and of lesional T cells, although this did not translate in changes in plaque size or stability features (apoptotic cell and macrophage content). The surprising lack in plaque phenotype despite the profound pro-atherogenic immune effects may be attributable to the sharp reduction of serum cholesterol levels in WTD fed bim−/− mice.